Particle size distribution is an important parameter in many processes and its accurate measurement is required for the precise and cost-effective control of the process. The measurement of particle size distribution in order to accurately control a process finds importance in industries that manufacture cement, cosmetics, pharmaceuticals and the like. A number of instruments are presently used in industry that use angular light scattering or dynamic light scattering techniques to measure particle size distribution in a liquid medium. These instruments analyze and measure the concentration of particles suspended in the liquid medium and provide a measurement that is used to adjust the process in order to correct for any irregularities in the final processed product. One such angular light scattering measurement instrument is taught in U.S. Pat. No. 5,416,580, to Trainer et al, issued May 16, 1995.
In order for these aforementioned instruments to measure correct particle size distribution, an extracted sample representative of the processed medium must be conditioned for measurement. Conditioning disperses the particles within the suspension into a concentration value that is within the concentration requirements of the measurement technique being utilized. The concentration of particles within a typical process is generally higher than is allowed by the measurement technique being utilized and the aforementioned conditioning introduces some form of dilution to disperse the concentration. For example, in the case of instruments that employ angular light scattering techniques, multiple scattering limits the concentration to less than 0.1% of particles in suspension. In the case of dynamic light scattering, particle-to-particle interactions limit concentration to less than 3%. Particle concentrations in a processed medium, however, can be as high as 50% by volume.
One method presently employed that overcomes these limitations is to deliver an extracted sample representative of the processed medium to a conditioning instrument, which works in association with the measurement instrument and dilutes, disperses and finally circulates the conditioned sample to the measurement instrument for analysis. After analysis, the diluted sample is discarded and the cycle repeated. Such conditioning instruments are taught in U.S. Pat. No. 4,496,244. to Ludwig et al, issued Jan. 29, 1985, and U.S. Pat. No. 5,439,288, to Hoffman et al, issued Aug. 8, 1995.
These arrangements have shortcomings in the need to transport a concentrated sample from the process location to the conditioning instrument, the time involved in the conditioning-circulating-flushing cycle and the final discarding of the dilute sample in preparation for the next sample extraction. Such conditioning instruments also suffer from poor reliability and excessive maintenance due inherently to the mechanical actions and motions of the multiple seals, valves and conduits that are required to extract the sample from the processed medium, condition the extracted sample and finally deliver the sample to the measurement instrument.